Apparatuses of the above-mentioned kind are already used today in a large number of variants where a specific article, especially a contact lens, is to be packed in a tightly sealed manner in a packaging. This is generally accomplished by introducing a contact lens into a depression of a base part of a packaging, dispensing a predetermined amount of a saline solution into the depression, then placing onto the packaging a cover film that can be thermally bonded to the base part of the packaging, and finally thermally bonding the cover film to the packaging. This operation may then be followed by sterilization. The packaging containing the contact lens can then be delivered to the customer or to the optician or ophthalmologist.
It will be readily apparent that especially in the field of the packaging of contact lenses, but also, for example, in the fields of foodstuffs, pharmaceuticals, medicinal articles and some other fields, certain requirements are to be met. Such requirements may relate especially to the sealing (against leakage or against the ingress of foreign substances) of the packaging, but they may also relate to the adhesion of the cover film to the base part of the packaging, to the impermeability of the packaging to certain substances, or to the force required to remove the cover film (peeling force). If a packaging is to be able to meet those requirements, the parameters during the thermal bonding of base part and cover film (duration, pressure, temperature) must always remain within predetermined limits and have to be reproducible.
Therefore, the adhesion of the cover film to the packaging must be such that it is sealed against the ingress of foreign substances from the outside and that it shall prevent the saline solution from leaking out. Furthermore, the packaging must not be damaged, for example, during the sterilization step, which normally takes place in an autoclave. In addition, the peeling force required to remove the cover film from the base part, that is to say to open the packaging, should not exceed a maximum value in order that the user is able to open the packaging with a reasonable amount of effort while ensuring the crucial sealing requirements discussed previously.
Apparatuses known in the art include a bonding head having a bonding contour support, a heatable bonding contour and a carrier. A rubber mount associated with the bonding head serves as a joint element and allows the bonding contour support to be tilted about axes that are perpendicular to guide bolts allowing for a linear displacement of the bonding head relative to the carrier.
This kind of apparatus has several disadvantages especially in respect of the above-mentioned demands that must be met when packaging contact lenses. In particular, the bonding head is prone to rotational movement as the rubber mount does not prevent rotational movement around the displacement axis along the guide bolts resulting in a twisting of the rubber mount which leads to a rotation of the bonding contour with respect to the packaging. Even slight rotation of the rubber mount may cause deficiencies in the sealing of the packaging preventing the packaging from meeting the strict requirements. Additionally, material fatigue of the rubber mount will have anticipated negative influence on the sealing quality of the device.
In order to meet the above mentioned requirements, the movement of the holding device and/or the bonding unit must be such that those surfaces of the holding device and of the bonding unit which transfer the sealing pressure to the packaging are very exactly parallel to one another while the orientation of the bonding contour with respect to the packaging must remain in an accurate predetermined position as even very slight fluctuations can result in significant variations in the sealing pressure and therefore in a seal that does not meet the requirements mentioned.